The technical report from the CSB concluded that a February 2014 spill at Tesoro's Martinez refinery resulted from insufficient tightening between a tube and a compression joint.

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The US Chemical Safety Board (CSB) released a technical
evaluation report on tubing samples taken from the Tesoro
refinery in Martinez, California, concluding that a sulfuric
acid spill on February 12, 2014, resulted from insufficient
tightening between a tube and a compression joint at a
sulfuric acid sampling station.

The spill burned two workers in the refinerys
alkylation unit, who were transported to the nearest hospital
burn unit by helicopter.

The spill continued for 2.5 hours, by which time an estimated
84,000 pounds of sulfuric acid was released from equipment
onto the refinery grounds and into a process sewer system.
Cal/OSHA ordered the process unit to remain shutdown from
February 18 until February 28 based on worker testimony that
the unit was unsafe.

The Cal/OSHA PSM Unit is also conducting a comprehensive
inspection at the Tesoro Refinery with an emphasis on
mechanical integrity and operating procedures.

The California Division of Occupational Safety and Health, or
Cal/OSHA, participated in this technical evaluation as part
of its regulatory investigation.

The incident occurred when the operators opened a block valve
to return an acid sampling system back to service. Very
shortly after this block valve had been fully opened, the
tubing directly downstream of the valve came apart, spraying
two operators with acid.

The report, prepared by Anamet -- a California-based
materials engineering and laboratory testing firm-- details
findings from laboratory examination of the stainless steel
tube assembly recovered by Cal/OSHA following the incident.
The report concludes that the sulfuric acid spill immediately
followed the failure of a 0.75-inch diameter stainless steel
tubing connector that came apart due to insufficient
tightening of the tube during installation.

The tube was being pressurized at the time of the incident,
and was part of a sulfuric acid sampling station in the refinerys alkylation unit.
The insufficient tightening between the tube and a
compression joint allowed the tube to be forced from the
joint, most likely by internal pressure.

Chemical analysis conducted on the tube assembly found that
all of its components, including the tube itself, are
constructed of Type 316 stainless steel. Type 316 stainless
steel is common in industrial processes that require a high
level of resistance to corrosion.

On March 10, 2014, in the same sulfuric acid alkylation unit,
two contract workers were sprayed with sulfuric acid while
conducting planned maintenance work to remove piping
in the alkylation unit. The sulfuric acid sprayed the two
workers when they cut into the piping using a portable band
saw.

The piping was not drained of process chemicals and was still
under pressure, despite the refinerys issuance of a
hot work permit for the activity, according to
the CSB. Although the contractors were wearing protective
suits while performing the work, they were still burned by
the acid.

One worker was exposed when his acid suit got caught on
scaffolding as he evacuated from the immediate area. The
second worker was burned when acid that remained on his acid
suit drained onto his neck during decontamination in the
safety shower.

Both workers were taken to a local hospital by ambulance for
evaluation and treatment for their chemical burn injuries.

This incident highlights the need for strong process
safety management at facilities that ensures mechanical
integrity is verified prior to the introduction of hazardous
chemicals into equipment," said CSB chairperson Rafael
Moure-Eraso. "However, on March 10, there was another
incident that also burned two workers with acid in the same
production unit. Four workers burned by sulfuric acid in less
than a month clearly demonstrates there are significant
opportunities within the refinery for improvement in safety
performance.

In the course of its investigation, the CSB said it
identified multiple incidents at the Martinez refinery over the past several
years involving the uncontrolled release of sulfuric acid.
These include chemical burns to a contract worker in June
2010, an August 2012 incident where two Tesoro workers were
sprayed with acid when a temporary hose ruptured and a
January 2012 acid release from a failed pump which injured
another worker.

The CSB is an independent federal agency charged with
investigating serious chemical accidents. The agency's
board members are appointed by the President and confirmed by
the Senate. CSB investigations look into all aspects of
chemical accidents, including physical causes such as
equipment failure as well as inadequacies in regulations,
industry standards, and safety management systems.

The board does not issue citations or fines but does make
safety recommendations to plants, industry organizations,
labor groups, and regulatory agencies such as OSHA and EPA

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Tubing used in any critical service such as acids , dry gas seals of compressors , is having inherent design with compression fittings , using ferrules typically single or double , based on plant standards of instrumentation tubing .To have safe operation and mechanical integrity of connection , many petrochemical / refinery installations refrain from using tubing ,and use piping with flanges along with required gaskets so that tightening of pipe is safe with no distortion of joint during tightening as part of design standards .

M.Nazir Chaudhry11.18.2014

For Better accident prevention, the followings steps should be taken in Sulphuric Acid application :1). All joints should be flanged instead of pressurized fittings2). If at all ,pressurized fitting is used, there must be covering sleeves on the joints3). Better Steel such as Alloy-20, Hastalloy-C etc. should be used instead of Stainless Steel

M.Nazir Chaudhry11.18.2014

Such type of accidents can be prevented if the sample tubing is of good alloy such as Hastalloy-C , Alloy-20 etc. and all piping joints should be overlapped with sleeves fitted on them.Moreover, after installation of tubing, the pressure terst should be done.It is further advisable to use flanged piping system instead of pressured Ferrule system in the Sulphuric Acid application.

ASHVIN MEHTA08.29.2014

In my opinion, the foremost issue is the type of the SS tube fitting, single ferrule versus double ferrule. The second issue here is installation of this SS tube fitting. Instrument technician should have followed the guidelines on installation details like, amount of torque and nos. of turns required to tighten the ferrule over tube, placing the ferrules correctly over the tube and lastly performing the leak/pressure test of the installation.

Marcos Menezes08.26.2014

The Stainless steel AISI 316 is poor in high corrosion is a problem the production ,is better AISI317L Corrosion Resistance high.same UHB Stainless34L or German W. Nr.1.4449 or AISI316+Nb , AISI316+Ti or ELC Stainless Steel UHB Stainless3Lor 3LN

stella Dominguez08.23.2014

No mentioning if the researchers look into the training program of the workers. Work instructions, mechanical integrity programs or any procedures are worthless if the end users are not trained. As well as the quantity of personnel available. Profit margins need to be met most of the time sacrificing the implementation of well written procedures.

John08.21.2014

What was the Tube Fitting Brand involved in the incidence please?Many a times instrumentation technicians forget to check if there are Ferrules or Olives in the fitting !